English 中文(简体)
有可能把第一种参数包 放在单线里吗?
原标题:Is it possible to get the first type of a parameter pack in a one-liner?
I have a parameter pack given in a variadic class template and want to extract the first type. Currently I do this, which works fine but is somehow cumbersome. Is it possible to do the same thing simpler? FirstEntityType should be defined to have the type of the first type in EntityTs. Note, I want to keep the signature of the class template. I know that it would be possible to write template, it is however something that I don t want to do. template struct EntityContext { template struct K { using type = T; }; using FirstEntityType = typename K::type; // ... };
最佳回答
You could write: using FirstEntityType = std::tuple_element_t<0, std::tuple>; Or you could use Boost.Mp11: using FirstEntityType = mp_front;
问题回答
You may use std::tuple_element<0, std::tuple>::type
In c++-26 it will be possible to simply write EntityTs...[0] see https://en.cppreference.com/w/cpp/language/pack_indexing




相关问题
Undefined reference

I m getting this linker error. I know a way around it, but it s bugging me because another part of the project s linking fine and it s designed almost identically. First, I have namespace LCD. Then I ...

C++ Equivalent of Tidy

Is there an equivalent to tidy for HTML code for C++? I have searched on the internet, but I find nothing but C++ wrappers for tidy, etc... I think the keyword tidy is what has me hung up. I am ...

Template Classes in C++ ... a required skill set?

I m new to C++ and am wondering how much time I should invest in learning how to implement template classes. Are they widely used in industry, or is this something I should move through quickly?

Print possible strings created from a Number

Given a 10 digit Telephone Number, we have to print all possible strings created from that. The mapping of the numbers is the one as exactly on a phone s keypad. i.e. for 1,0-> No Letter for 2->...

typedef ing STL wstring

Why is it when i do the following i get errors when relating to with wchar_t? namespace Foo { typedef std::wstring String; } Now i declare all my strings as Foo::String through out the program, ...

C# Marshal / Pinvoke CBitmap?

I cannot figure out how to marshal a C++ CBitmap to a C# Bitmap or Image class. My import looks like this: [DllImport(@"test.dll", CharSet = CharSet.Unicode)] public static extern IntPtr ...

Window iconification status via Xlib

Is it possible to check with the means of pure X11/Xlib only whether the given window is iconified/minimized, and, if it is, how?

热门标签